Optimize npm build

[havenchyk]

It doesn't make sense to deliver everything to the end user

[dwmkerr]

Awesome, thanks so much! Makes it much cleaner this way 😄

[havenchyk]

@dwmkerr it doesn't change a lot, but delivers less files so I feel it's more correct.

But I also noticed there is an opposite opinion like inspect-js/object-inspect#33 (review)

so please be aware of it as well 😄

but e.g. eslint doesn't follow this convention and uses "files" https://github.com/eslint/eslint/blob/master/package.json#L36-L43

[dwmkerr]

I agree - npm install should deliver the code required to use the package. If I want to run the tests, etc etc, I would clone and run them. So totally on board with this approach (frankly I think that this is much more correct this way as we don't pollute the consumer's node_modules with internal elements they shouldn't have to care about).